1. Technical Field of the Invention
The present invention relates generally to structure maneuvering and more particularly to a control apparatus for slewing maneuvers of flexible structures.
2. Discussion of the Related Art
It is often desired to actuate a flexible structure in a slewing maneuver. Example applications include robot links manipulators such as the Remote Manipulator System (RMS), solar panels, actual and simulated space structures, etc. Several gearing devices have been used for transmitting the actuator torques to maneuver flexible structures during a given operation and in general these gearing devices have the shared drawback of non-varying gear ratios. A constant gear ratio is the consequence of using circular gears having proportional circumferences. In applications where gear rotational space is at a premium, a constant ratio imposes a significant spatial requirement.
A gear train, which is made of a series of circular gears, magnifies the torque of the actuator at a given constant gear ratio. The gear train can be accompanied by a roller chain or belt drive for transmitting the torque over a distance. This configuration results in undesirable backlash and suffers from excessive inertia and friction. A harmonic drive provides for very high gear-ratios to result in high drive torques with very low backlashes. However, this drive also has a constant gear ratio.
Special linkage, direct drive mechanisms can replace the role of the complex gear train or roller chain drives in robot manipulators. Two kinds of direct-drive mechanisms have been extensively used for the rigid-body robots, namely a four-bar parallel linkage and a five-bar polygon-type linkage. The direct-drive linkages are driven by two actuators located in parallel or in series, directly transmit the torques to the manipulators instead of through gear trains or roller chains, so that the actuator torques are decoupled through the direct-drive mechanisms to simplify the rather complicatedly coupled multi-body dynamics that mutually interact during the control process. The linkages of these direct drive mechanisms generate considerable inertia which must be considered in the dynamics of, e.g., robots. Also, gravity can effect these linkages and accordingly necessitates a more complicated control system. Finally, these linkages occupy a considerable amount of precious work space.